1. Field of the Invention
The present invention relates to an internal combustion-engined setting tool for driving fastening elements, such as, e.g., bolts, nails, etc. . . . into a constructional component and including at least one main combustion chamber, a piston guide adjoining the main combustion chamber, a drive piston displaceably supported in the piston guide and displaceable in a setting direction by expandable gases produced in the main combustion chamber upon ignition of a compressible fuel filling the main combustion chamber, a pre-chamber for generating a pressure that is transmitted to the main combustion chamber before the ignition of the air-fuel mixture in the main combustion chamber takes place.
2. Description of the Prior Art
Setting tool of the type described above can be operated with gaseous or evaporated liquid fuels which are combusted in a combustion chamber for driving a setting piston that drives the fastening elements in.
In the setting tools of the type described above, It is desirable to achieve the most possible thermal efficiency.
German Publication DE-4243617A1 discloses a setting tool in which beneath the drive piston, in the setting direction, a pre-combustion space is provided in an axiliary cylinder. In its initial position, the drive piston is located immediately above the precombustion space and is spaced from the main combustion chamber. The pre-compression of the air-fuel mixture in the main combustion chamber is effected in the setting tool of DE-4243617A1 by ignition of the air-fuel mixture that fills the pre-combustion space, whereby the piston is accelerated toward the main combustion chamber, which leads to an isentropic compression of the air-fuel mixture above the drive piston and in the main combustion chamber.
The drawbacks of the setting tool of DE-4243617A1 consist in that it is constructively very complex and requires additional space for additional chambers, and in that manufacture of its is associated with very high costs.
Accordingly, an object of the present invention is to provide an internal combustion-engined setting tool of the type described above in which the drawbacks of the known setting tool are eliminated and a high thermal efficiency is achieved.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a pre-chamber which is formed by space within the piston guide and beneath a bottom of the drive piston remote from the main combustion chamber when the drive piston occupies its initial position, and a transfer channel for communicating the pre-chamber and the main combustion chamber.
Hence, it is suffice for the pre-chamber be formed by the expansion space of the drive piston within the piston guide. The expansion space is defined as space within the piston guide beneath the bottom of the drive piston when the drive piston is in its initial position and adjoins the bottom of the main combustion chamber. By using the piston expansion space as a pre-chamber, the increase of pressure in the main combustion chamber can be achieved during a setting process without a need in additional space and complex mechanical measures.
Between the pre-chamber and the main combustion chamber, a transfer channel is provided through which the pressure medium produced in the pre-chamber can flow into the main combustion chamber, which results in pressure increase in the main combustion chamber. Providing a transfer channel between the pre-chamber, which can be formed, e.g., by the expansion space of the drive piston in the piston guide, and the main combustion chamber permits to provide a construction that can be easily and cost-effectively produced and that, at the same time, is characterized by a high thermal efficiency due to the precompression of the air-fuel mixture in the main combustion chamber.
It is very advantageous when the pre-chamber is formed as a combustion chamber in which an air-fuel mixture is ignited, with the combustion gases and, eventually, flame front flowing through the transfer channel into the main combustion chamber where they provide for increase of pressure therein and, eventually, the turbulence. In the main combustion chamber, the air-fuel mixture, which fills the chamber, becomes pre-compressed and is ignited after a predetermined pressure is reached.
In the transfer channel, there is provided a valve, in particular, a check valve that provides for medium flow from the pre-chamber into the main combustion chamber but that prevents the medium flow in the opposite direction. In particular, the check value closes the transfer channel immediately after the air-fuel mixture in the main combustion chamber has been ignited.
According to a further modification of the present invention, advantageously, the pre-chamber is divided in two chambers, a pre-combustion chamber in which an air-fuel mixture can be ignited, and a pressure chamber which contains air by the point in time at which ignition in the pre-combustion chamber takes place. Advantageously, the pre-combustion chamber and the pressure chamber are separated by a plate. Ideally, the separating plate is displaceably supported on the piston rod of the drive piston and is sealed against the piston guide and the piston rod. Upon the ignition of the air-fuel mixture in the pre-combustion chamber, the separating plate is displaced under the pressure of the generated explosion gases in the direction toward the pressure chamber, so that the pressure in the pressure chamber increases. The pressure increase in the pressure chamber leads to opening of the valve in the transfer channel, and the air flows from the pressure chamber into the main combustion chamber, increasing pressure therein.
Advantageously, there are provided, in the main combustion chamber, detection means, which can be formed, e.g., as a sensor for detecting pressure in the main combustion chamber, and ignition means for igniting the air-fuel mixture in the main combustion chamber and actuatable in response to the detection means detecting a predetermined pressure in the main combustion chamber, which pressure is increased as a result of flow of medium from the pre-chamber into the main combustion chamber. In this way, the ignition of the air-fuel mixture in the main combustion chamber can be effected automatically, without intervention of a user.
It is advantageous when the valve means in the transfer channel is so formed that it provides for flow of not only gas or vapor-forming medium but also provides for passage of a reaction front, e.g., a flame front from the pre-chamber or the pre-combustion chamber into the main combustion chamber. This measure permits to effect, in a simple manner, the ignition of the air-fuel mixture in the main combustion chamber by overflow of the flame front together with the pressure front from the pre-chamber.
To provide for a permanent pressure increase, there is provided magnetic holding means for retaining the drive piston in its initial position with a predetermined holding force.
The magnetic holding means can be arranged either in the region of the main combustion chamber or in the region of the piston guide. The holding force is so selected that the pressure increase in the main combustion chamber, as a result of overflow of medium from the pre-chamber, by itself does not provide for displacement of the drive piston from its initial position. The release and displacement of the drive piston in the setting direction takes place only upon the ignition of the air-fuel mixture in the main combustion chamber and as a result, upon a further increase of pressure therein, with the further increased pressure overcoming the holding force of the magnetic means.
Advantageously, a mouth opening of the transfer channels opens into the pre-chamber immediately beneath the drive piston when the drive piston is in its initial position. Thereby, the transfer channel becomes closed immediately, after the release of the drive piston.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.